Various properties are required for a ball such as a basketball, handball, rugby ball, or American football. For example, surface abrasion resistance at high level is required for a surface material subjected to repeated rubbing or collision with a hand, a floor, or the like. Further, in a case where a ball is brought into direct contact with a hand, soft cushioning property is required for reducing impact on fingertips in catching of the ball.
Various methods have been hitherto proposed as a method of obtaining a ball having cushioning property.
For example, there are proposed: a leather-like sheet at least including 4 layers of a nonporous elastic polymer layer (first layer), a porous elastic polymer layer (second layer), a layer formed of an elastic polymer and a nonwoven fabric (third layer), and a nonwoven fabric layer (fourth layer); and a ball formed of the leather-like sheet (see Patent Document 1). However, in a method of Patent Document 1, the first and second layers were formed by using elastic polymers each having durability for practical use to provide a ball which had insufficient cushioning property and which could not be suitably used as a ball for sports such as basketball.
Further, there is proposed synthetic leather having a transparent nonporous layer containing polyurethane as a main ingredient laminated on a surface of a base fabric covered with a polyurethane layer and having a pattern of pebbles and valleys. The synthetic leather has an air layer between the valleys and the nonporous layer, and a total area of bonding parts between the pebbles and the nonporous layer accounts for 50 to 90% of a surface area of the synthetic layer (see Patent Document 2). However, even in Patent Document 2, a ball having both cushioning property and durability for practical use and used as a ball handled by a hand such as a basketball has not yet been obtained.
A ball such as a basketball requires non-slip property to improve usability. There is proposed a basketball with excellent non-slip property including 9 to 12 cover panels and groove forming members for joining the cover panels on an outer surface of a ball main body (see Patent Document 3). However, sufficient non-slip property is hardly obtained because an area ratio of the groove forming members is small at joining parts of the cover panels in Patent Document 3.
Further, there is proposed a basketball having numerous polygonal recesses on an outer surface (see Patent Document 4). However, such polygonal recesses cause a ball formed of a sheet containing a base fabric to have poor softness, cushioning property, and feel. Further, the ball has problems in that abrasion resistance in collision with a ground is reduced and that a ball surface gets dirty easily.
In addition, there is proposed a basketball having numeral specific dimples on an outer surface (see Patent Document 5). According to Patent Document 5, the dimples have a height difference between projections and recesses of 200 to 500 μm, a vertical projected area of each of adjoining recesses of 79 to 314 mm2 (diameter of 10 to 20 mm), and an average distance between the recesses of 8 to 16 mm ( 5/16 to ⅝ inches). However, such large dimples cause a ball formed of a sheet containing a base fabric to have problems such as reduced abrasion resistance, and poor cushioning property and non-slip property.
Further, there is proposed a sweat-absorbing ball material having a wet-coagulated polyurethane cover layer laminated on a surface of a polyurethane-impregnated fibrous material, in which the cover layer has a plurality of projecting pebbles and valleys between the pebbles on the surface thereof, and side surfaces of the pebbles are perforated (see Patent Document 6). However, the material of Patent Document 6 gets dirty easily, and dirt accumulates in use over a long period of time, to thereby significantly deteriorate a non-slip effect, impede its use, and provide insufficient cushioning property.
Therefore, a ball having sufficient surface abrasion resistance, cushioning property, and non-slip property was desired.
Patent Document 1: JP-A-2000-102629
Patent Document 2: JP-A-11-093081
Patent Document 3: JP-A-2003-117026
Patent Document 4: U.S. Pat. No. 4,991,842
Patent Document 5: U.S. Pat. No. 5,518,234
Patent Document 6: U.S. Pat. No. 6,024,661